Radio apparatus



Feb. 24, 1942.

c. F. sHEAr-'FER RADIO APPARATUS Filed Nov. 15, 1941 Patented Feb. 1942 UNITED STATES PATENT OFFICE'.

RADIO APPARATUS Charles vF. Sheaffer, Tulsa, Okla. Application November 15, 1941, Serial No. 419,332

12 Claims.

This invention relates to electrical circuits generally. More particularly this invention relates to frequency stabilizing and adjustingsystems and frequency deviation indicators.

An object of this invention .is to provide a frequency discriminating device, the rectified output of which is a direct current voltage, whose polarity andamplitude. is directly proportional to the frequency deviation and direction of deviation between an oscillator of fixed frequency and an oscillator, the frequency of which is to be controlled, or the deviation, from the xed frebe apparent to those skilled in the art to which it relates from the following specification and the claims. A

In accordance with this invention I provide two beat frequency detectors for the purpose of deriving `the beat frequency between two oscillators, the frequency of one of which is more or less fixed and the frequency of the other subject to variation, the magnitude of which it Kis desired to limit and/o r indicate by metering de- Vice. In addition a phase shifting device is used to shift the phase of one of the oscillators before applicationto one of the beat detectors, this being for the purpose of displacing the phase of the two beat detector outputs by 90 degrees. A further phase shift is provided tor one of the beat detector, outputs which gives an additional shift l of 90 degrees and renders the shifted beat output a direct function -of Lthe frequency. Under the above circumstances a phase turnover of 180 portional to the frequency deviationand direction of deviation of the frequency of the oscillator subject to variation from the frequency of the reference oscillator.

Further details of my invention will be apparent from the following 4specification and drawing in which, the sole gure illustrates an em bodiment of my invention.

Oscillator A is a regenerative vacuum tube os- (Cl. Z50-36) cillator utilizing a. tuned circuit as the frequency determining element. 'I'he reactance tube B forms a part of the frequency determining circuit of A and thereby permits the `frequency of the 5 oscillator A to be controlled by the bias voltage supplied to the grid of the reactance tube device B. This combination is conventional and has been described in various publications.

Oscillator A supplies a radio frequency voltage through condenser I to grid G1 of vacuum tube 8.

'. It also supplies, through condenser 3, grid G1 of.

vacuum tube 9. Crystal oscillator C, which is a convengonal device, utilizing a vacuum tube osf /cillato/r in which a quartz crystal forms the frequency determining element, supplies a radio frequency voltage to grid G2 of tube 8. It also supplies the phase shifting network` D which shifts the phase of the crystal frequency by exactly 90 electrical degrees and supplies the shifted output to grid G2 of vacuum tube 9. Yacuum tubes 8 and 9 are mixer-detector devices, the purpose of which is to derive a beat frequency equal to the difference in frequency between oscillators A and C. For the purpose of illustration let it be assumed that the frequency of oscillator C is exactly 1000 kilocycles.

effects of temperature variation and circuit instability. For example assume that the frequency of oscillator A becomes 1001 kilocycles. In this event, a beat frequency of 1000 cycles appears across resistor i0 in the plate circuit of detector E and across resistor l5 in the plate circuit of detector F.

The beats in the plate circuits of tubes 8 and 9 occur as a result of the falling in and out of step of the two radio frequency voltages when the phase of one of them is advancing at a greaterrate than the other, which of course, is a re- Isult of a frequency difference. The phase displacement aiforded by shifter D therefore causes a 90 degrees phase 'displacement between the two beat frequency sources at the plates of detectors E and F. If, now, the frequency of oscillator A becomes, for instance, 999 kilocycles, the phase relation between the beats will be reversed due to'the fact that the phase of oscillator A is now continuously retarding with respect to that-ofV oscillator C, whereas, when the frequency of oscillator A was 1001 kilocycles, its phase was continuously advancing with respect to that of os cillator4 C. If, for instance, the phase relation between the -beat supplies from detectors E and F may be represented vectorially by the expression: V=:Vf, when the frequency of oscillator A is higher than 1000 kilocycles, then the expression indicating the phase relation between the 00 beats when the frequency of oscillator A'is lower than 1000f'ki1ocycles becomes: V=iV1. In

these expressions, V designates voltage and sub letters e and f indicate respectively the outputs of detectors E and F. The phase reversal indicated -occurs at zero-beat, since it is dependent upon whether the phase of oscillator A is advancing, or retardingfwith respect to that of oscillator C.

'I'he purpose of network G is to provide an additional phase displacement of 90 degrees between the two beat frequency supplies and to provide an output, the amplitude of which, is

proportional to the frequency. Network G is therefore interposed between :the plate of detector tube 9 and the grid circuit of tube 22. Coil has no appreciable reactance at the beat frequencies, but effectively chokes out radio frequency from the oscillators.

Connection is made from the plate of tube 8 through resistor II and choke I3 to the grid of The purpose and characteristics of choke I3 are identical with that of choke coil tube 2|.

20. Resistor I2 returns resistor II to ground through bias battery I4. The combination Il, I2 and I4 provides the correct alternating voltage level and proper bias for tube 2|.

The voltages at the grids of tubes 2I and 22 will/asia Vresult oflthepreviousllexplained phase 'to terminal 24d which is a center tap on the sec- .ondary of transformer 24. Terminal 24e connects to the plate of rectifier tube 25 and 24e connects to the plate ofrectifier tube 26. The return made from terminal 23e through resistors 2l and'28 .to the respective cathodes of tubes 25 the beat frequency and its polarity is dependent I not pass direct current, the output of detector J will be zero. If the frequency of oscillator A deviates. a resulting beat frequency is applied to the balanced rectifier J from separate sources through transformers 23 and v24. 'I'he amplitude of the source from'transformer 23 does not vary withthe beat frequency, but the amplitude of the beat frequency delivered by transformer 24 is directly proportional to the frequency. therefore the voltage output of the detector J will depend uponthe extent to which the voltage from the secondary of transformer 24 can unbalance the voltage applied to the two rectifier plates from the secondary of transformer 23. In other words, the unbalance, and hence the balanced detector output is directly proportional to upon the phase relation of the beat sources, which reverses yas the frequency difference goes through zero-beat.

The output of rectifier J is apulsating direct current voltage and its pulsations are ltered out by condensers 29 and 3I in conjunction with resistor 30. The voltage across condenser 3| is therefore a pure direct current voltage whose polarity and amplitude are dependent directly.

upon the deviation and direction of deviation of the frequency of the oscillator A. This voltage and 26. Rectifier 25 rectiiiesthe series voltages f -supplied by the secondary-of transformer 23 and half of the secondary of transformer 24, the output of which appears across resistor 21. Rectier tube 25 is so connected that it recties the series voltages from the secondary of transformer 23 and the other half ofthe secondary of transformer 24. Y' The output of this rectifier appears acrossresistor 28. The connectionsare so made that if the phases of the voltages'from ampliflers H and Iv are such that the voltages in series with terminals 23e and.24c are in phase,

then, the voltages in series with terminals 23e and 24e will be in phase opposition.

The output connectionffrom the balanced rectiiier J is made between the cathodes of tubes 25 n fductor I8 in series, will be called Er.

and 26. With this connection the rectified volti age at the output will be zero if the voltages ap- A plied vto the plates of tubes 25 and 25 equal. It

of oscillator A is equal to that of oscillator C, the

beat outputs of detectors E and F will have zero frequency and since transformers 23 and 24 canis supplied to the grid of the reactance control tube B which directly and automatically limits the possible frequency deviation of the oscillator A. W V- Transformers 23 and 24 are high grade iron core devices capable of delivering constant amplitude response throughout a frequency band extending from 15 to 15,000 cycles. The transformers, as well as other components are selected to make the phase shift 'characteristics of amplifiers H and I identical.

Milliammeter 34 in conjunction with resistory cuit will be assumed, in which the plate resistance of tube 9 and resistor I5 will be combined and called Rp. An equivalent driving voltage will be assumed to be in series with Rp and will be called Eg. The alternating voltage resulting across .the combination of resistor I1 and in- The angular frequency in radians per second will 'be designated by w, andthe condenser I6, the resistor I1 and the Inductor I8 ,will be indicated, in the analysis, as` respectively C, R and L.

'I'he vector resultingy from the derivation of the ratio Ef/Eg yields the angle of phase shift. Y The equation for this is given b y (l).

g.: (man (l) E. R+R +j wL-1/w0 Rationalizing Equation l yields Equation 2, beI low.

1mm If the numerator of the first lterm of Equation 2 could be equated to zero for all frequencies, the network G would shift the phase of any fre.- quency passed through it by exactly degrees.

This, of course, is not, possible. However, suppose that the frequency band of importance extends only to 15,000 cycles, and that in this band, the components are selected so that l/wC; c-L. In this case the numerator of the rst term of Equation 2 will reduce to: R(R-|Rp) -L/C. This expression does not vary with the frequency, and may therefore be equated to zero for frequencies within the band extending from zero to 15,000 cycles.

A further requirement is that'Ei/Eg be a linear function. 'I'his means that the second term of Equation 2 must be directly proportional to the frequency. To illustrate that circuit component's may be selected to suf'ciently meet this requirement, we now consider the result of selecting values so that: R+Rp)2(1/wC)2. Equation A2 then reduces to: Ef/Eg-fwCR. This expression is perfectly linear.- In practice, it has been found that the last above condition need not be stringently met in order to obtain satisfactory linearity,

In the circiut arrangement shown diode typel rectifier tubes may be used to replace the mixer type tubes used in detectors E and F, and vthe network G may be placed in the plate circuit of detector E instead of the plate circuit of detector F.

4 While I have described this invention in detail in a prefer-red embodiment, it will be observed that modifications therein may be made without departing from the spirit and scope thereof and therefore I intend to be limited only as indicated by the scope of the following claims.

Having'described my invention I claim:

1. In a frequency stabilizing and adjusting system the combination of, a source of radio frequency oscillations, the frequency of whichA is substantially fixed, a second source of radio fre-` 90 degrees, amplifiers yfor amplifying the two separate beat frequency oscillations, a balanced ,rectier, means for impressing said beat frequency oscillations on said rectifier in such a manner that the output of said rectifier` will be zero iflthe frequen-cy of the two sources of radio frequency oscillation are equal, and will be a positive or negative voltage proportional to the frequency difference if the radio frequency oscillations have unequal frequency, and means for controlling the frequency of said second source in accordance with the output-of, said rectifier.

2. In a frequency stabilizing and adjusting system the combination of, a source of radio fre.- quency oscillations, the frequency of which is substantially fixed, a second source of radio frequency oscillations having a frequency subject to variation, the: extent of which is to be controlled,

` two detector devices eachof said detector devices` deriving a beat frequency between the frequencies of said sources o f radio frequency oscillations, means for shifting the phase of one of said oscillation sources lby substantially 90 degrees before application thereof to one of said detectors, a network for shifting the phase of one of the beat frequency oscillations by substantially 90 degrees,

a rectifier, means for impressing said beat frequency oscillations. on said rectifier in s-uch a manner that the output of said-rectifier will be zero if the frequency of the two sources of radio frequency oscillation are equal, and will be a positive or negative voltage proportional to the frequency difference if the radio frequency oscillations have unequal frequency, and means for controlling the frequency of said second source in accordance with the output of said rectifier.

3. In a frequency stabilizing and adjusting system the combination of, a' source of radio frequency oscillations, the frequency of which is substantially fixed, a second source of radio frequency oscillations having a frequency subject to variation, the extent of which is to be controlled, two detector devices each of said detector devices deriving a beat frequency between the frequencies of said sources of radio frequency oscillations, means for shifting the 'phase of one of said oscillation sources by substantially 90 degrees before application thereof to one of said detectors, a network for shifting the phase.

of one of the beat-frequency oscillations .by substantially 90\degrees, amplifiers for amplifying impressing said beat frequency oscillations on said rectifier in such a manner that the output of said rectifier will be zero if the frequency of the two sources of radio frequency oscillation are equal, and will be a positive or negative voltage proportional to the frequency difference if the radio frequency oscillations have unequal frequency, and means for controlling the frequency of said second source in accordance with the output of said rectifier.

4. In a frequency stabilizing and adjusting system the combination of, a source of radio frequency oscillations, the frequency of which is substantially fixed, a second source of radio frequency oscillations having av frequency subject to variation, the extent of which is to be controlled, two detector devices each of said detector devices deriving a heat frequency between the frequencies of said sources of radio frequency oscillations, means for shifting the phase of one of said oscillation sources by substantially 90 degrees before application thereof to one of said detectors, a network for shifting the phase of one ,of the beat frequency oscillations by substantially 90 degrees, a balanced rectifier, transformer means for impressing said beat frequency oscillations on said rectifier in `such a manner `vthat the output of said rectifier will be/zero if the frequency of the two'sourceslof radio frequency oscillation are equal, and will be a positive or negative voltage proportional to the frequency difference if the radio frequency oscillations have unequal frequency, .and means for controlling the frequency of said secondsource in accordance with theA outputl of said rectifier. 5. In a frequency stabilizing and adjusting system the combination of, a source of radio frequency oscillations, the frequency of which is substantially fixed, a-second source of radio frequency oscillations having a frequency subject to variation, the extent of which is to be controlled, two detector devices, each? of said detector devices deriving a beat frequency be- 4 tween the frequencies of said sources of radio frequency oscillations, means'for shifting the phase-of one of said oscillation sources by substantially 90 degrees before application thereof to one o f said detectors, a network for shifting the phase of one of the beat frequency oscillations by substantially 90 degrees, amplifiers for amplifying the two separate beat frequency oscillations, a-balanced rectifier, means for impressing said beat frequencyvoscillations on said rectifier 4in such a manner that the output of said rectifier will be zero if the frequency of the two sources of radio frequency oscillation are equal, and will be positive or negative voltage proportional to the frequency difference if the radio frequency oscillations have unequal frequency, the polarity of said voltage depending upon whether the frequency of the oscillation source subject to' variation is higher or lower than that of the fixed source of oscillation, a variable reactance tube device for controlling the frequency of said variable -source of oscillations,

l,means for filtering and applying the output of said balanced rectifier to said variable reactance tube device for the purpose of exerting a controlling inuence on the frequency of said second source of radio frequencyoscillation.

6. In a frequency stabilizing andadjustng system the combination of, a source of radio frequency oscillations, the frequency of -which is substantially fixed, a second source of radio frequency oscillations having a frequency subject to variation, the extent of which is to be controlled, two detector devices, each of said detector devices deriving a vbeat frequency between the frequencies of said sourcesl of radio frequency oscillations, means for shifting the phase of one of said oscillation sources by substantially 90 degrees before application thereof to one of said detectors, a network for shifting the phase of one of the beat frequency oscillations by substantially 90 degrees, a rectier, means for impressing said beat frequency oscillationson said of radio frequency oscillation are equal,v and will be positive or negative voltage proportional to the frequency difference if the radio frequency oscillationsA have unequal frequency, the polarity o f said voltage-depending upon whether the frequency of the oscillation source subject to variation is higher or lower than that of the fixed source of oscillation, a variable reactance tube device for controlling the frequency of said variable source of oscillations, means for lterin'g and applying the output of said balanced rectier to said variable reactance tube device for the purpose of exerting a controlling influence on the frequency of said second source of radio frequency oscillation.

8. In a frequency stabilizing and adjusting system the combination of, a source of radio frequencyoscillations, the frequency of which isl substantially fixed, a second source of radio frequency oscillations having a frequency subject to variation, the extent of. which is to be controlled, two detector devices, each of said detector devices deriving a beat frequency between the frequencies of vsaid sources of radio frequency oscillations, means for shifting the phase of one of said oscillation sources by substantially 90 degrees before application thereof to one of said detectors, a network for shifting the phase of one of the beat frequency oscillations by substantially 90 degrees, ampliers for amplifying the two sep- 4 arate beat frequency oscillations, a balanced recrectifier in such a manner that the output of .i

said rectifier will be zero if the frequency of the two `sources of radio frequency oscillation are equal, and will be positive or negative voltage proportional to the frequency difference if the radio frequency oscillations have unequal frequency, the polarity of said voltage depending tube device for the purpose of exerting a controllin'g influence on the frequency of said second source'of radio frequency oscillation.

7. In a frequency stabilizing and adjustingystem the combination of. a sourceof radio frequency oscillations, the frequency of which is and will be Apositive or negative voltage proportional to the frequency difference if the radio frequency oscillations have unequal frequency, the polarity of said .voltage depending upon whether the frequency of the oscillation source4 subject to variation ishigher or lower than thatl of the fixed source of oscillation, a variable reactance tube device for controlling the frequency of said variable source of oscillations, means for filtering 'and applying the output of said balanced 'rectifier to said variable reactance tube `device substantially fixed, a second source of radio frequencyoscillations having a frequency subject to variation, the extent of which is'to be controlled,

two detector devices, each of said detector devices deriving a beat frequency between the frequencies of said sources lof radio frequency oscillations, meansfor shifting the phase of one of said oscillation sources by substantially 90 degrees for the purpose of exerting a controlling influence on the frequency of said second source of radio frequency oscillation.

9. The combination of two sources of radio frequency oscillations, the frequency of one of which issubstantially constant and the frequency of the other subject to variation. the extent of `which is to be'controlled, two detector devices for deriving v the beat frequency between said sources of oscillation, means for shifting the phase of one of said sources of radio frequency oscillations before application thereof to the corresponding beat detector, said beat frequency oscillations being displaced `in phase by substantially 90 degrees, a

vphase shifter adapted to shift the phase of one rectifier provides a voltage whichv is a pulsating direct current voltage proportional to the fre- -quency difference between the said sources ofradio frequencyoscillations and the polarity of which` depends upon which of said sources of radio frequency oscillation exceeds the other in frequency.

10. The combination of two sources of radioy frequency oscillations, the frequency of one of which is substantially constant and the frequency of the other subject to variation, the extent of which is to be controlled, two detector devices for deriving the beat frequency between said sources of oscillation, means for shifting the phase of one of said sources of radio frequency oscillations before application thereof to the corresponding beat detector, said beat frequency oscillations being displaced in phase by substantially 90degrees, a phase shifter adapted to shift the phase of one of said beat frequency oscillations by apthe output of one of said beat detectors, a rectifier supplied by both of said beat frequency oscillations, means for lvarying the amplitude of one of I said frequencyoscillations so that the output of said rectifier provides a voltage which is a pulsating direct current voltage proportional to the frequency difference between the said sources of radio frequency oscillations and the polarity of "which depends upon which of said sources of proximately 90 degrees connected to the'output of one of said beat detectors, a `rectifier supplied by both of said beat frequency oscillations, means for varying the amplitude of one of said beat frequency loscillations so that the output of said rectifier provides a voltage which is a pulsating direct current voltage proportional to the frequency differenceA between the said sources of radio frequency oscillations and the polarity of which depends upon which ofsaid sources of radio frequency oscillation exceedsl the other in frequency, and means for controlling vthe frequency of said variable source in accordance with said direct current voltage.

11. The combination of two sources of radio frequency oscillations, the frequency of one of radio frequency oscillations exceeds the other in frequency, means for filtering said pulsating direct current voltage, and means controlled by said filtered direct current voltage for con.

l trolling the frequency of said variable frequency source.

12'. AThe combination of two sources of radio frequency oscillations, the frequency of one of which is substantially constant and thefrequency `of the other subject' to variation, the extent of which is to be controlled, two detector devices for deriving the beat frequency between said sources of oscillation, means for shifting the phase of one of said sources of radio frequency oscillations beforev application thereof to the corresponding beat detector, said beat frequency oscillations .being displaced in phase by substantially 90 degrees connected to the output of one of said beat detectors, a rectifier supplied by both. of said beat which is substantially constant and the frequency v of the other subject to variation, the extent of which is to be controlled, two detector devices,

frequency oscillations, means for varying the amplitude of one of said beat frequency oscil-k lations so that the output of said rectifier provides a voltage which is a pulsating direct current voltage proportional to the frequency difference between the said sources of radio frequency oscillations andthe polarity of which depends upon which of said sources of radio frequency oscillation exceeds the other in frequency. means for filtering said pulsating direct current voltage, and a variable reactance4 tube connected to said last means for controlling the frequency of said variable frequency oscillator in` accordance with said filtered direct current voltage. v HEAFFE CHARLES F. S R. 

